A 17-year before and after experiment in Puget
Sound that used a hatchery conservation program to aid a distressed stock of
wild steelhead resulted in more redds (nests) even after supplementation ended
and provided the naturally produced stock with stable or increasing
measurements of genetic diversity, according to a recent study.
The Hamma Hamma River that flows down the
eastern slopes of the Olympic Mountains and into the Hood Canal has just 3.6
kilometers (2.2 miles) of habitat that can be reached by anadromous fish.
Before supplementation or captive breeding had begun the stream supported a
mean of 10 steelhead redds. After supplementation the number had risen to a
mean of 26 redds, the study says.
The study also drew on four control streams
with steelhead in the same area, showing that the rise in the number of redds
in the Hamma Hamma was solely due to careful supplementation.
Even after supplementation ended, the number
of redds remained high, according to study author Barry Berejikian, supervisory
research fisheries biologist at NOAA Fisheries’ Northwest Fisheries Science
Center, Manchester Research Station.
“The number of redds (compilation of nests)
constructed by natural-origin female steelhead in the supplemented population
(Hamma Hamma) was 2.6 times greater in the generation after the supplemented
program was terminated than it was before the program,” Berejikian said.
“Samples from juveniles collected in the supplemented population indicated an
increase in the effective number of breeders from 24.4 in the generation before
supplementation to 38.9 after supplementation. Other measures of genetic
diversity remained stable or increased.”
The four non-supplemented control populations
monitored over the same 17 year period exhibited stable or decreasing trends in
redd abundance, he said. Control streams were the Little Quilcene (10 before
the supplementation period, 14 after), North Fork Skokomish (30 before, 29
after), Tahuya 123 before, 37 after) and Union 31 before, 9 after).
Declines in abundance of Puget Sound steelhead
began in the late 1980s, followed by a listing as threatened under the federal
Endangered Species Act in 2007.
The methods used in the Hamma Hamma
supplementation program were non-conventional, Berejikian said. The program was
designed specifically to benefit the natural population, and avoid some of the
known and perceived shortcomings of typical supplementation programs.
“Supplementation programs have the greatest
opportunity to benefit natural populations if they are well-conceived by having
very clearly defined biological objectives, consider the properties and
limiting factors of the natural population, take into consideration recent
findings about promising broodstock, rearing and release strategies, and have
some level of monitoring and accountability,” he said.
“Increased natural reproduction and genetic
diversity one generation after cessation of a steelhead trout (Oncorhynchus
mykiss) conservation hatchery program” was published online Jan. 19, 2018 in
the journal PLOS/One, http://journals.plos.org/plosone/article/comments?id=10.1371/journal.pone.0190799. Berejikian’s co-author is Donald Van Doornik, research fisheries
biologist, also at NOAA’s Manchester Research Station.
According to the study, “captive propagation
programs have contributed to successful maintenance or amplification of some
endangered populations, however, the genetic risks associated with captive
propagation, and challenges associated with reintroduction raise the critical
question of whether populations would fare better if left alone. Captive
propagation efforts initially intended as temporary measures may become
long-term endeavors if the factors causing declines are not adequately
Some programs have prevented extinction and
still maintain genetic diversity through carefully planned breeding protocols
and are trending toward self-sustaining populations, the study says.
“How a supplementation program impacts the
viability of natural populations (positively or negatively) will likely depend
on important details of specifically how the program is operated,” Berejikian
said. “The best approaches may not be the most convenient. Clearly defined
rationale and goals are perhaps the most important components in establishing
and evaluating supplementation programs.”
In the Hamma Hamma program, the duration of
supplementation was always intended to be finite, and it was concluded as
planned, he said
“Additional studies of this type are needed to
determine when and how supplementation can provide some benefit to natural
populations,” Berejikian said. “For example, populations that are below
capacity (under-escaped) because of poor marine survival conditions may be more
positively influenced by supplementation, but we have very few cases where
programs have been terminated and monitored post-supplementation. The results
of this study are encouraging, but habitat improvements are obviously still needed
to recover natural steelhead populations.”
A recently published long-term study of Idaho
supplementation programs had mixed results. It found that after 22 years
supplementation in two Idaho drainages increased chinook salmon abundance at
some life stages, but the effects did not persist after supplementation of
hatchery stock ceased and had no apparent influence on productivity.
See CBB, January 12, 2018, “Long-Term Idaho
Salmon Supplementation Study Delivers Mixed Results; Not A Stand-Alone Recovery
Tool,” http://www.cbbulletin.com/440072.aspx, and “Effects of hatchery supplementation on abundance and
productivity of natural-origin Chinook salmon: two decades of evaluation and
implications for conservation programs,” Dec. 4, 2017, Canadian Journal of
Fisheries and Aquatic Sciences (http://www.nrcresearchpress.com/doi/abs/10.1139/cjfas-2016-0344#.WlecN6inHIU).